The present patent application is directed to the art of battery charging and, more particularly, to systems and methods for charging and pulsating batteries in online battery backup systems.
Battery backup systems are employed to provide uninterrupted power to electronic equipment when power from the electric grid fails. When such backup systems charge and discharge, various products are generated by the electro-chemical reactions which take place within the battery cells, and thermodynamic forces may cause those products to gradually alter to a more stable but less reactive form. For example, the discharge of a lead-acid battery produces an amorphous form of lead sulfate which may crystallize to form non-conductive deposits that are resistant to decomposition at charging and equalization voltages. Another example: charging a nickel-cadmium battery produces microcrystalline forms of hydroxyl—nickel oxide and metallic cadmium (serving as the anode and cathode, respectively, of the cell), but these materials tend to coalesce and/or grow to form larger crystalline deposits which can slow electro-chemical reaction rates due to mass transfer limitations at the electrode/electrolyte interface.
The accumulation of deposits such as those described above tends to degrade the capacity of the battery backup system by, depending upon the chemistry and construction of the cell, (1) reducing the amount of active material in the battery cell, (2) blocking the active material in an electrode from the electrolyte in the battery cell, and/or (3) increasing cell resistance. If sufficient deposits accumulate, the battery backup system may be unable to provide sufficient power due to a decline in voltage and/or loss of storage capacity in the battery cells, causing the powered electronic equipment to malfunction or prematurely fail.
Devices have been developed to counteract the accumulation of such deposits through the application of pulsation energy, generally in the form of radio frequency (RF) energy, during the charging of a battery or battery string. However, the batteries of an online battery backup system typically serve as a continuously connected source of power, operating in parallel with the electric grid in order to eliminate switchover time and reduce potential points of failure. If a battery pulsation device were to be used in an online battery backup system protecting critical or sensitive electronic equipment such as telecommunications equipment, the pulsation energy applied to the batteries may cause unacceptable levels of electro-magnetic interference (EMI) to be conducted and/or radiated into that equipment, interfering with its proper operation. Consequently, online battery backup systems require more frequent battery string replacements, whether of individual cells or the entire string, to maintain acceptable levels of reliability. However the application of pulsation energy would beneficially complement both offline and online management techniques by increasing battery service life, potentially lengthening the intervals between maintenance periods, and potentially shortening the time during which the battery string of the battery backup system is bypassed for maintenance.
Accordingly there is a need for a system and method for applying pulsation energy to online battery backup systems that includes features to limit or reduce the transmission of EMI into powered electronic equipment.